Numerous processes exist for fabricating thermoplastic composite parts. In addition to non-continuous processes such as pressing, stamping and autoclave forming, there are continuous processes such as extrusion, pultrusion, roll forming, and compression molding. Examples of continuous fabrication processes for forming straight and curved, continuous length, thermoplastic composite parts having various cross-section configurations are shown in commonly-owned U.S. Pat. No. 7,807,005 (Rubin et al.), U.S. Pat. No. 7,871,553 (Wilkerson et al.) and U.S. Pat. No. 8,333,858 (Rubin et al.), each of which is incorporated in its entirety by reference herein.
The foregoing processes find applicable uses in a wide variety of potential applications including, for example, in the aerospace industry. The processes may be ideally suited for fabricating thermoplastic composite parts, such as stiffened members in the supporting framework of an aircraft fuselage. Examples of thermoplastic composite stiffened members include but are not limited to fuselage skins, wing skins, control surfaces, door panels, access panels, keel beams, floor beams and deck beams.
In a typical implementation of a continuous compression molding (CCM) process for fabricating thermoplastic composite parts, one or more unconsolidated thermoplastic plies is covered on both sides with stainless steel foils or kapton layers to form a thermoplastic composite material blank, which is fed into a CCM process assembly. The CCM process assembly may have a pre-forming unit and a press or consolidation unit provided in sequential relationship with respect to each other. Other units may be included to provide, for example, a curvature along the length of the parts or other shapes or features into the part's pressed shape, or the pre-forming unit or consolidation unit may be configured to provide such features.
The pre-forming unit of the CCM process assembly may have an intake end adapted to receive a continuous supply of flat or planar thermoplastic composite material blank in any defined layup, for example, in the form of spool-rolled material which may be wound on one or multiple spools or, alternatively, in the form of stacked material. The pre-forming unit has forming surfaces that form the thermoplastic composite material blank into a pre-formed laminate having a selected cross-section configuration. The pre-forming unit may use a variety of forming surfaces and have any design known to those skilled in the art suitable for imparting the selected cross-section configuration to the thermoplastic composite material blank.
The pre-formed laminate having the selected cross-section configuration exits the pre-forming unit and enters the consolidation unit of the CCM process assembly, where the one or multiple plies in the pre-formed laminate are consolidated to form a single, pressed and integrated thermoplastic composite part, such as the stiffened members described above, using the application of heat and pressure. Referring to FIG. 1, for example, a consolidation unit may include one or more matched sets of tooling dies 1 that may be mated with the forming surfaces of the pre-forming unit. An upper tooling die 2 in the matched sets of tooling dies 1 is provided with a first contoured surface 3 matching the contour of an upper surface 4 of the pre-formed laminate 5 (which is shown advancing between the tooling dies 1). A lower tooling die 6 is provided with a second contoured surface 7 complementary to the first contoured surface 3 and matching the contour of a lower surface 8 of the pre-formed laminate 5. The tooling dies 1 may be coupled to mechanical, electrical, hydraulic, pneumatic or other types of actuators (not shown), which move the upper tooling die 2 and lower tooling die 6 toward and away from each other between an extended, tool-closed position (as shown in FIG. 1) and a retracted, tool-open position. As the pre-formed laminate 5 moves between the upper tooling die 2 and lower tooling die 6, the pre-formed laminate 5 is heated and the tooling dies 1 provide pressure sufficient to consolidate the thermoplastic plies in the pre-formed laminate 5 into a desired shape and thickness.
It has been determined that when a pre-formed laminate 5 has a cross-section configuration with two or more bends, and three or more segments, such as the “hat” shaped cross-section configuration shown in FIG. 1, the stainless steel foils or kapton layers surrounding one or both sides of the thermoplastic plies in the pre-formed laminate 5 may get trapped by angled side segments 9 of the tooling dies 1 as the pre-formed laminate 5 is advanced into and through the tooling dies 1. This prevents the pre-formed laminate 5 from slipping well along the surfaces 3, 7 of the tooling dies 1, and may cause wrinkles 10 to form in the foils and/or the pre-formed laminate 5. Wrinkling of the foils and/or pre-formed laminate 5 reduces part quality and increases scrap rate and production costs. There is therefore a need to improve processing techniques and facilities to enable fabrication of thermoplastic composite parts without wrinkles in the composite material or the foil or kapton material layers, to decrease scrap rate and production costs, and increase part quality and other efficiencies.